[libwebm] Add unit test builders Current https://build.webmproject.org/jenkins/view/webm/job/libwebm__test/ has different cpu architecture and sanitizer configuration for each test. Change-Id: I08bf6a70224e456a9f28e48af0bd2312b47f8d8a Bug: b:185520494 Reviewed-on: https://chromium-review.googlesource.com/c/codecs/infra/+/3057617 Reviewed-by: James Zern <[email protected]>